Download Chemical Compounds Chemical Compounds

Chemical
Compounds
Ionic and Covalent
Compounds . . . . . . . . . 374
Internet Connect . . . . 376
Acids, Bases,
and Salts . . . . . . . . . . . 377
QuickLab . . . . . . . . . . 380
Biology Connection . . 381
Internet Connect . . . . 382
Organic Compounds . . 383
Biology Connection . . 386
Internet Connect . . . . 389
Chapter Review . . . . . . . . . . 392
Feature Articles . . . . . . 394, 395
LabBook . . . . . . . . . . . . 688–691
Something’s Fishy
Pre-Reading
Questions
Some people keep saltwater aquariums as a hobby. The living organisms in these aquariums—fish, coral, and algae—
must have the correct environment, or they might die.
Many things must be controlled in the aquarium. For
example, the pH of the water must stay within a certain
range. The amount of salt and other compounds in the
water also must be within a certain range. In this chapter,
you will learn about pH. You will also learn about salts and
other chemical compounds.
1. What is the difference
between ionic compounds
and covalent compounds?
2. What is an acid?
3. What is a hydrocarbon?
372
Chapter 15
Copyright © by Holt, Rinehart and Winston. All rights reserved.
STICKING TOGETHER
In this activity you will demonstrate
the force that keeps particles
together in some compounds.
Procedure
1. Blow up two balloons. Rub them
with a piece of wool cloth.
2. Hold the balloons by their necks.
Move the balloons near each
other. Describe in your ScienceLog
what you see.
3. Put one of the balloons against a
wall. Record your observations in
your ScienceLog.
Analysis
4. The balloons are charged by rubbing them with the wool cloth.
Like charges repel each other.
Opposite charges attract each
other. Infer whether the balloons
have like or opposite charges.
Explain your answer.
5. The two types of charge are negative and positive. The balloon in
step 3 has a negative charge. Infer
what the charge is on the wall
where you put the balloon. Explain.
6. The particles that make up some
compounds are attracted to each
other in the same way that the balloon is attracted to the wall. What
can you infer about the particles that
make up such compounds?
Chemical Compounds
Copyright © by Holt, Rinehart and Winston. All rights reserved.
373
Section
1
ionic compounds
covalent compounds
◆ Describe the properties of ionic
and covalent compounds.
◆ Classify compounds as ionic
or covalent based on their
properties.
Ionic and Covalent
Compounds
The world around you is made up of chemical compounds.
Chemical compounds are pure substances composed of ions
or molecules. There are millions of different kinds of compounds, so you can imagine how classifying them might be
helpful. One simple way to classify compounds is by grouping them according to the type of bond they contain.
Figure 1 An ionic compound is formed when
the metal sodium reacts
with the nonmetal
chlorine. Sodium chloride is formed in the
reaction, and energy is
released as light and
thermal energy.
Figure 2 Ionic compounds will shatter
when hit with a hammer.
374
Ionic Compounds
Compounds that contain ionic bonds are
called ionic compounds. Remember that
an ionic bond is the force of attraction
between two oppositely charged ions.
Ionic compounds can be formed by the
reaction of a metal with a nonmetal.
Electrons are transferred from the metal
atoms (which become positively charged
ions) to the nonmetal atoms (which
become negatively charged ions). For
example, when sodium reacts with chlorine, as shown in Figure 1, the ionic compound sodium chloride, or ordinary table
salt, is formed.
Brittleness The forces acting between
the ions that make up ionic compounds
give these compounds certain properties.
Ionic compounds tend to be brittle, as
shown in Figure 2. The ions that make
up an ionic compound are arranged in
a repeating three-dimensional pattern
called a crystal lattice. The ions that make
up the crystal lattice are arranged as alternating positive and negative ions. Each
ion in the lattice is surrounded by ions
of the opposite charge, and each ion is
bonded to the ions around it. When an
ionic compound is struck with a hammer,
the pattern of ions in the crystal lattice is
shifted. Ions with the same charge line up
and repel one another, causing the crystal to shatter.
Chapter 15
Copyright © by Holt, Rinehart and Winston. All rights reserved.
High Melting Points Ionic compounds are almost always solid at
room temperature, as shown in
Figure 3. An ionic compound will
melt only at temperatures high
enough to overcome the strong
ionic bonds between the ions.
Sodium chloride, for instance,
must be heated to 801°C before it
will melt. This temperature is
much higher than you can produce in your kitchen or even your
school laboratory.
Magnesium oxide
melts at 2,800°C.
Nickel(II) oxide
melts at 1,984°C.
Potassium dichromate
melts at 398°C.
Solubility and Electrical Conductivity
Many ionic compounds dissolve easily in water. Molecules of water attract each
of the ions of an ionic compound and pull them away from
one another. The solution created when an ionic compound
dissolves in water can conduct an electric current, as shown
in Figure 4. The ions are able to move past one another and
conduct the electric current in the solution. Keep in mind that
an undissolved crystal of an ionic compound does not conduct
an electric current.
Pure water
Figure 3 Each of these ionic
compounds has a high melting
point and is solid at room
temperature.
Salt water
Figure 4 The pure water in the left beaker does not conduct
an electric current. The solution of salt water in the right beaker
conducts an electric current, and the bulb lights up.
Covalent Compounds
Compounds composed of elements that are covalently bonded
are called covalent compounds. Remember that covalent
bonds form when atoms share electrons. Gasoline, carbon
dioxide, water, and sugar are well-known examples of covalent compounds.
Chemical Compounds
Copyright © by Holt, Rinehart and Winston. All rights reserved.
375
Low Melting Points Covalent compounds exist as independent particles called molecules. The forces of attraction between
molecules of covalent compounds are much weaker than the
bonds between ions in a crystal lattice. Thus, covalent compounds have lower melting points than ionic compounds.
Molecules of covalent compounds can have anywhere
from two atoms to hundreds
or thousands of atoms!
Small, lightweight molecules, like water or carbon
dioxide, tend to form liquids
or gases at room temperature. Heavier molecules,
such as sugar or plastics,
tend to form solids at room
temperature.
Solubility and Electrical Conductivity You have probably
heard the phrase “oil and water don’t mix.” Oil, such as that
used in salad dressing, is composed of covalent compounds.
Many covalent compounds do not dissolve well in water. Water
molecules have a stronger attraction for one another than they
have for the molecules of most other covalent compounds.
Thus, the molecules of the covalent compound get squeezed
out as the water molecules pull together. Some covalent compounds do dissolve in water. Most of these solutions contain
uncharged molecules dissolved in water and do not conduct
an electric current, as shown in Figure 5. Some covalent compounds form ions when they dissolve in water. Solutions of
these compounds, including compounds called acids, do conduct an electric current. You will learn more about acids in
the next section.
Figure 5 This solution of sugar, a
covalent compound, in water does
not conduct an electric current
because the individual molecules
of sugar are not charged.
Sugar water
REVIEW
1. List two properties of ionic compounds.
NSTA
TOPIC: Ionic Compounds,
Covalent Compounds
GO TO: www.scilinks.org
sciLINKS NUMBER: HSTP355, HSTP360
2. List two properties of covalent compounds.
3. Methane is a gas at room temperature. What type of compound is this most likely to be?
4. Comparing Concepts Compare ionic and covalent
compounds based on the type of particle that makes
up each.
376
Chapter 15
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Section
2
acid
base
pH
salt
◆ Describe the properties and uses
of acids and bases.
◆ Explain the difference between
strong acids and bases and
weak acids and bases.
◆ Identify acids and bases using
the pH scale.
◆ Describe the properties and uses
of salts.
Acids, Bases, and Salts
Have you ever noticed that when you
squeeze lemon juice into tea, the color
of the tea becomes lighter? Shown in
Figure 6, lemon juice contains a substance called an acid that changes
the color of a substance in the
tea. The ability to change the
color of certain chemicals is one
property used to classify substances as acids or bases. A third
category of substances, called
salts, are formed by the reaction of an acid with a base.
Figure 6 Acids, like those
found in lemon juice, can
change the color of tea.
NEVER
touch or taste
a concentrated
solution of a
strong acid.
Acids
An acid is any compound that increases the number of hydrogen ions when dissolved in water, and whose solution tastes
sour and can change the color of certain compounds.
Properties of Acids If you have ever had orange juice, you
Figure 7 Bubbles of hydrogen
gas are produced when zinc
metal reacts with hydrochloric acid.
have experienced the sour taste of an acid. The taste of lemons,
limes, and other citrus fruits is a result of citric acid. Taste,
however, should NEVER be used as a test to identify an unknown
chemical. Many acids are corrosive, meaning they destroy body
tissue and clothing, and many are also poisonous.
Acids react with some metals to produce hydrogen gas, as
shown in Figure 7. Adding an acid to baking soda or limestone
produces a different gas, carbon dioxide.
Solutions of acids conduct an electric current because acids
break apart to form ions in water. Acids increase the number
of hydrogen ions, H+, in a solution. However, the hydrogen ion
does not normally exist alone. In a water solution, each hydrogen ion bonds to a water molecule, H2O, to form a hydronium
ion, H3O+.
Chemical Compounds
Copyright © by Holt, Rinehart and Winston. All rights reserved.
377
Detecting Acids As mentioned earlier, a property of acids is
Some hydrangea plants act
as indicators. Leaves on the
plants change from pink to
blue as the soil becomes
more acidic.
their ability to change the color of a substance. An indicator
is a substance that changes color in the presence of an acid
or base. An indicator commonly used is litmus. Paper strips
containing litmus are available in both blue and red. When
an acid is added to blue litmus paper,
the color of the litmus changes to
red, as shown in Figure 8. (Red litmus paper is used to detect bases,
as will be discussed shortly.) Many
plant materials, such as red cabbage, contain compounds that
are indicators.
Figure 8 Vinegar turns blue litmus
paper red because it contains
acetic acid.
Uses of Acids Acids are used in many areas of
Figure 9 The label on this car
battery warns you that sulfuric
acid is found in the battery.
industry as well as in your home. Sulfuric acid is
the most widely produced industrial chemical in
the world. It is used in the production of metals,
paper, paint, detergents, and fertilizers. It is also
used in car batteries, as shown in Figure 9. Nitric
acid is used to make fertilizers, rubber, and plastics. Hydrochloric acid is used in the production
of metals and to help keep swimming pools free
of algae. It is also found in your stomach, where
it aids in digestion. Citric acid and ascorbic acid
(vitamin C) are found in orange juice, while carbonic acid and phosphoric acid help give extra
“bite” to soft drinks.
Strong Versus Weak As an acid dissolves in water, its molecules break apart and produce hydrogen ions. When all the
molecules of an acid break apart in water to produce hydrogen
ions, the acid is considered a strong acid. Strong acids include
sulfuric acid, nitric acid, and hydrochloric acid.
When few molecules of an acid break apart in water to
produce hydrogen ions, the acid is considered a weak acid.
Acetic acid, citric acid, carbonic acid, and phosphoric acid are
all weak acids.
378
Chapter 15
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Bases
A base is any compound that increases the number of hydroxide ions when dissolved in water, and whose solution tastes bitter, feels slippery, and can change the color of certain compounds.
Properties of Bases If you have ever accidentally tasted soap,
then you know the bitter taste of a base. Soap also demonstrates that a base feels slippery. However, NEVER use taste or
touch as a test to identify an unknown chemical. Like acids,
many bases are corrosive. If your fingers feel slippery when you
are using a base in an experiment, you might have gotten the
base on your hands. You should immediately rinse your hands
with large amounts of water.
Solutions of bases conduct an electric current because bases
increase the number of hydroxide ions, OH⫺, in a solution. A
hydroxide ion is actually a hydrogen atom and an oxygen atom
bonded together. An extra electron gives
the ion a negative charge.
Detecting Bases
Like acids, bases
change the color of an indicator. Most
indicators turn a different color for bases
than they do for acids. For example,
bases will change the color of red litmus
paper to blue, as shown in Figure 10.
To determine how acidic or
basic a solution is, just use
your head—of cabbage!
Try it for yourself
on page 688 of
the LabBook.
NEVER
touch or taste
a concentrated
solution of a
strong base.
Figure 10 Sodium hydroxide,
a base, turns red litmus
paper blue.
Uses of Bases Like acids, bases have many uses. Sodium
hydroxide is used to make soap and paper. It is also in oven
cleaners and in products that unclog drains, as shown in
Figure 11. Remember, bases can harm your skin, so carefully
follow the safety instructions when using these products.
Calcium hydroxide is used to make cement, mortar, and plaster. Ammonia is found in many household cleaners and is also
used in the production of fertilizers. Magnesium
hydroxide and aluminum hydroxide are
used in antacids to treat heartburn.
Figure 11 This drain cleaner
contains sodium hydroxide to
help dissolve grease that can
clog the drain.
379
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Strong Versus Weak
When all the molecules of a base break
apart in water to produce hydroxide ions, the base is called a
strong base. Strong bases include sodium hydroxide, calcium
hydroxide, and potassium hydroxide.
When only a few of the molecules of a base produce
hydroxide ions in water, the base is called a weak base.
Ammonia, magnesium hydroxide, and aluminum hydroxide
are all weak bases.
Acids and Bases Neutralize
One Another
Figure 12 Have heartburn? Take
an antacid! Antacid tablets contain a base that neutralizes the
acid in your stomach.
If you have ever suffered from an acid stomach, or heartburn,
as shown in Figure 12, you might have taken an antacid.
Antacids contain weak bases that soothe your heartburn by
reacting with and neutralizing the acid in your stomach. Acids
and bases neutralize one another because the H⫹ of the acid
and the OH⫺ of the base react to form water, H2O. Other ions
from the acid and base are also dissolved in the water. If the
water is evaporated, these ions join to form a compound called
a salt. You’ll learn more about salts later in this section.
The pH Scale
pHast Relief!
1. Fill a small plastic
cup halfway with
vinegar. Test the
vinegar with red
and blue litmus
paper. Record your
results in your
ScienceLog.
2. Carefully crush an antacid
tablet, and mix it with the
vinegar. Test the mixture
with litmus paper. Record
your results in your
ScienceLog.
3. Compare the acidity of the
solution before and after
the reaction.
380
Indicators such as litmus can identify whether
a solution contains an acid or base. To describe how acidic or
basic a solution is, the pH scale is used. The pH of a solution
is a measure of the hydronium ion concentration in the solution. By measuring the hydronium ion concentration, the pH
is also a measure of the hydrogen ion concentration. On the
scale, a solution that has a pH of 7 is neutral, meaning that
it is neither acidic nor basic. Pure water has a pH of 7. Basic
solutions have a pH greater than 7, and acidic solutions have
a pH less than 7. Look at Figure 13 to see the pH values for
many common materials.
Figure 13 pH Values of Common Materials
Increasing acidity
1
2
3
Lemon
juice
4
5
Increasing basicity
6
Milk
Soft
drink
Human
saliva
7
8
9
10
11
Sea Detergents
water
12
13
Household
ammonia
Tap water
Acid rain
Clean rain
Human stomach contents
Chapter 15
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Using Indicators to Determine pH A single
indicator allows you to determine if a solution
is acidic or basic, but a mixture of different
indicators can be used to determine the pH of
a solution. After determining the colors for
this mixture at different pH values, the indicators can be used to determine the pH of an
unknown solution, as shown in Figure 14.
Indicators can be used as paper strips or solutions, and they are often used to test the pH of
soil and of water in pools and aquariums. Another
way to determine the acidity of a solution is to use
an instrument called a pH meter, which can detect
and measure hydrogen ions electronically.
Figure 14 The paper strip contains
several indicators. The pH of a solution
is determined by comparing the color
of the strip to the scale provided.
Self-Check
Which is more acidic, a soft drink or milk? (Hint:
Refer to Figure 13 to find the pH values of these
drinks.) (See page 724 to check your answer.)
pH and the Environment Living things depend on having a steady pH in their environment. Plants are known
to have certain preferred growing conditions. Some plants,
such as pine trees, prefer acidic soil with a pH between 4
and 6. Other plants, such as lettuce, require basic soil with
a pH between 8 and 9. Fish require water near pH 7.
As you can see in Figure 13, rainwater can have
a pH as low as 3. This occurs in areas where
compounds found in pollution react
with water to make the strong acids
sulfuric acid and nitric acid. As this
acid precipitation collects in lakes,
it can lower the pH to levels that
may kill the fish and other organisms in the lake. To neutralize the
acid and bring the pH closer to 7,
a base can be added to the lakes,
as shown in Figure 15.
Biology
C O N N E C T I O N
Human blood has a pH of between
7.38 and 7.42. If the pH is above 7.8
or below 7, the body cannot function
properly. Sudden changes in blood
pH that are not quickly corrected can
be fatal.
Figure 15 This helicopter is adding a
base to an acidic lake. Neutralizing the
acid in the lake might help protect the
organisms living in the lake.
Chemical Compounds
Copyright © by Holt, Rinehart and Winston. All rights reserved.
381
Salts
When you hear the word salt, you probably think of the table
salt you use to season your food. But the sodium chloride
found in your salt shaker is only one example of a large group
of compounds called salts. A salt is an ionic compound formed
from the positive ion of a base and the negative ion of an
acid. You may remember that a salt and water are produced
when an acid neutralizes a base. However, salts can also be
produced in other reactions, as shown in Figure 16.
Figure 16 The salt potassium
chloride can be formed from
several different reactions.
Figure 17 Salts are used to help
keep roads free of ice.
Uses of Salts Salts have many uses in industry and in your
home. You already know that sodium chloride is used to season foods. It is also used in the production of other compounds, including lye (sodium hydroxide), hydrochloric acid,
and baking soda. The salt calcium sulfate is made into wallboard, or plasterboard, which is used in construction. Sodium
nitrate is one of many salts used as a preservative in foods.
Calcium carbonate is a salt that makes up limestone, chalk,
and seashells. Another use of salts is shown in Figure 17.
REVIEW
1. What ion is present in all acid solutions?
NSTA
TOPIC: Acids and Bases, Salts
GO TO: www.scilinks.org
sciLINKS NUMBER: HSTP365, HSTP370
2. What are two ways scientists can measure pH?
3. What products are formed when an acid and base react?
4. Comparing Concepts Compare the properties of acids and
bases.
5. Applying Concepts Would you expect the pH of a solution
of soap to be 4 or 9?
382
Chapter 15
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Section
Organic Compounds
3
Of all the known compounds, more than 90 percent are members of a group of compounds called organic compounds.
Organic compounds are covalent compounds composed of
carbon-based molecules. Sugar, starch, oil, protein, nucleic acid,
and even cotton and plastic are organic compounds. How can
there be so many different kinds of organic compounds? The
huge variety of organic compounds is explained by examining the carbon atom.
organic compounds
biochemicals
proteins
carbohydrates
nucleic acids
lipids
hydrocarbons
◆ Explain why so many organic
compounds are possible.
◆ Describe the characteristics of
Each Carbon Atom Forms Four Bonds
carbohydrates, lipids, proteins,
and nucleic acids and their functions in the body.
◆ Describe and identify saturated,
unsaturated, and aromatic
hydrocarbons.
Carbon atoms form the backbone of organic compounds.
Because each carbon atom has four valence electrons (electrons in the outermost energy level of an atom), each atom
can make four bonds. Thus, a carbon atom can bond to one,
two, or even three other carbon atoms and still have electrons
remaining to bond to other atoms. Three types of carbon backbones on which many organic compounds are based are shown
in the models in Figure 18.
Some organic compounds have hundreds or even thousands of carbon atoms making up their backbone! Although
the elements hydrogen and oxygen, along with carbon, make
up many of the organic compounds, sulfur, nitrogen, and
phosphorus are also important—especially in forming the molecules that make up all living things.
Figure 18 These models, called structural formulas, are used
to show how atoms in a molecule are connected. Each line
represents a pair of electrons shared in a covalent bond.
H
H C H
H
H
H
H
H
C
C
C
C
C
H
H
H
H
H
H
H
H
H
H
Straight Chain All carbon
atoms are connected one
after another in a line.
H
C H
C H H
C
C H
C H H
H C H
H
Branched Chain The chain of carbon
atoms continues in more than one direction where a carbon atom bonds to three
or more other carbon atoms.
H
H
C
H
C H
C H
C
H
H
H H
H C
H C
Ring The chain of carbon
atoms forms a ring.
Chemical Compounds
Copyright © by Holt, Rinehart and Winston. All rights reserved.
H
383
Biochemicals: The Compounds of Life
Organic compounds made by living things are called
biochemicals. The molecules of most biochemicals are very
large. Biochemicals can be divided into four categories: carbohydrates, lipids, proteins, and nucleic acids. Each type of
biochemical has important functions in living organisms.
Carbohydrates
Starch and cellulose are examples of carbohydrates. Carbohydrates are biochemicals that are composed
of one or more simple sugars bonded together; they are used
as a source of energy and for energy storage. There are two
types of carbohydrates: simple carbohydrates and complex
carbohydrates. A single sugar molecule, represented using a
hexagon, or a few sugar molecules bonded together are examples of simple carbohydrates, as illustrated in Figure 19.
Glucose is a simple carbohydrate produced by plants through
photosynthesis.
Figure 19 The sugar molecules
in the left image are simple
carbohydrates. The starch in the
right image is a complex carbohydrate because it is composed
of many sugar molecules
bonded together.
Sugar Storage System When an organism has more sugar
than it needs, its extra sugar may be stored for later use in
the form of complex carbohydrates, as shown in Figure 19.
Molecules of complex carbohydrates are composed of
hundreds or even thousands of sugar molecules
bonded together. Because carbohydrates provide
the energy you need each day, you should
include sources of carbohydrates in your
diet, such as the foods shown in Figure 20.
Figure 20 Simple carbohydrates
include sugars found in fruits and
honey. Complex carbohydrates,
such as starches, are found in
bread, cereal, and pasta.
384
Chapter 15
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Lipids
Fats, oils, waxes, and steroids are examples
of lipids. Lipids are biochemicals that do not
dissolve in water and have many different
functions, including storing energy and
making up cell membranes. Although
too much fat in your diet can be
unhealthy, some fat is extremely
important to good health. The foods
in Figure 21 are sources of lipids.
Lipids store excess energy in the
body. Animals tend to store lipids
primarily as fats, while plants store
lipids as oils. When an organism has
used up most of its carbohydrates, it
can obtain energy by breaking down
lipids. Lipids are also used to store vitamins
that dissolve in fat but not in water.
Figure 21 Vegetable oil, meat,
cheese, nuts, and milk are
sources of lipids in your diet.
Lipids Make Up Cell Membranes Each cell is surrounded
by a cell membrane. Much of the cell membrane is formed
from molecules of phospholipids. The structure of these molecules plays an important part in the phospholipid’s role in
the cell membrane. The tail of a phospholipid molecule is a
long, straight-chain carbon backbone composed only of carbon and hydrogen atoms. The tail is not attracted to water.
The head of a phospholipid molecule is attracted to water
because it is composed of phosphorus, oxygen, and nitrogen
atoms in addition to carbon and hydrogen atoms. This results
in the double layer of phospholipid molecules shown in the
model in Figure 22. This arrangement of phospholipid molecules creates a barrier to help control the flow of chemicals
into and out of the cell.
Deposits of the lipid cholesterol in the body have been
linked to health problems
such as heart disease.
However, cholesterol is
needed in nerve and brain
tissue as well as to make
certain hormones that regulate body processes such
as growth.
Figure 22 A cell membrane is
composed primarily of two layers
of phospholipid molecules.
The head of each phospholipid
molecule is attracted to water
either inside or outside of the cell.
The tail of each phospholipid
molecule is pushed against
other tails because they are
not attracted to water.
Chemical Compounds
Copyright © by Holt, Rinehart and Winston. All rights reserved.
385
Proteins
Figure 23 Meat, fish, cheese,
and beans contain proteins,
which are broken down into
amino acids as they are digested.
Most of the biochemicals found in living things are
proteins. In fact, after water, proteins are the most abundant
molecules in your cells. Proteins are biochemicals that are
composed of amino acids; they have many different
functions, including regulating chemical activities,
transporting and storing materials, and providing
structural support.
Every protein is composed of small “building
blocks” called amino acids. Amino acids are smaller
molecules composed of carbon, hydrogen, oxygen,
and nitrogen atoms. Some amino acids also include
sulfur atoms. Amino acids chemically bond to form
proteins of many different shapes and sizes. The function of a protein depends on the shape that the bonded
amino acids adopt. If even a single amino acid is missing or
out of place, the protein may not function correctly or at all.
The foods shown in Figure 23 provide amino acids that your
body needs to make new proteins.
Examples of Proteins
Biology
C O N N E C T I O N
All the proteins in your body are
made from just 20 amino acids.
Nine of these amino acids are called
essential amino acids because your
body cannot make them. You must
get them from the food you eat.
Enzymes are proteins that regulate
chemical reactions in the body by acting as catalysts to increase
the rate at which the reactions occur. Some hormones are proteins. Insulin is a hormone that helps regulate the level of sugar
in your blood. Oxygen is carried by the protein hemoglobin,
allowing red blood cells to deliver oxygen throughout your
body. There are also large proteins that extend through cell
membranes and help control the transport of materials into
and out of cells. Proteins that provide structural support often
form structures that are easy to see, like those in Figure 24.
Figure 24 Hair and
spider webs are
made up of proteins
that are shaped like
long fibers.
386
Chapter 15
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Nucleic Acids The largest molecules made by living organisms are nucleic acids. Nucleic acids are biochemicals that store
information and help to build proteins and other nucleic acids.
Nucleic acids are sometimes called the “blueprints of life”
because they contain all the information needed for the cell
to make all of its proteins.
Like proteins, nucleic acids are long chains of smaller molecules joined together. These smaller molecules are composed
of carbon, hydrogen, oxygen, nitrogen, and phosphorus atoms.
Nucleic acids are much larger than proteins even though
nucleic acids are composed of only five building blocks.
Science
C O N N E C T I O N
Nucleic acids store information—even
about ancient peoples. Read more
about these incredible biochemicals
on page 394.
DNA and RNA There are two types of nucleic acids: DNA
and RNA. DNA (deoxyribonucleic acid), like that shown in
Figure 25, is the genetic material of the cell. DNA molecules
can store an enormous amount of information because of
their length. The DNA molecules in a single
human cell have an overall length of
about 2 m—that’s over 6 ft long! When
a cell needs to make a certain protein, it copies the important part
of the DNA. The information
copied from the DNA directs
the order in which amino acids
are bonded together to make
that protein. DNA also contains
information used to build the
second type of nucleic acid, RNA
(ribonucleic acid). RNA is involved
in the actual building of proteins.
Figure 25 The DNA from
a fruit fly contains all of the
instructions for making proteins,
nucleic acids . . . in fact, for
making everything
in the organism!
REVIEW
1. What are organic compounds?
2. What are the four categories of biochemicals?
3. What are two functions of proteins?
4. What biochemicals are used to provide energy?
5. Inferring Relationships Sickle-cell anemia is a condition
that results from a change of one amino acid in the
protein hemoglobin. Why is this condition a genetic
disorder?
Chemical Compounds
Copyright © by Holt, Rinehart and Winston. All rights reserved.
387
Hydrocarbons
Organic compounds that are composed of only carbon and
hydrogen are called hydrocarbons. Hydrocarbons are an important group of organic compounds. Many fuels, including gasoline, methane, and propane, are hydrocarbons. Hydrocarbons
can be divided into three categories: saturated, unsaturated,
and aromatic.
Saturated Hydrocarbons
Propane, like that used in the stove
in Figure 26, is an example of a saturated hydrocarbon. A
saturated hydrocarbon is a hydrocarbon in which each carbon
atom in the molecule shares a single bond with each of four
other atoms. A single bond is a covalent bond that consists of one pair of shared electrons. Hydrocarbons
that contain carbon atoms connected only by sinH H H
gle bonds are called saturated because no other
H C C C H
atoms can be added without replacing an atom
H H H
that is part of the molecule. Saturated hydrocarbons are also called alkanes.
Unsaturated Hydrocarbons
Figure 26 The propane in this
camping stove is a saturated
hydrocarbon.
Figure 27 Fruits produce ethene,
which helps ripen the fruit. Ethyne,
better known as acetylene, is
burned in this miner’s lamp and is
also used in welding.
H
H
C C
Each carbon atom forms four
bonds. However, these bonds do not always have to be single bonds. An unsaturated hydrocarbon is a hydrocarbon in
which at least two carbon atoms share a double bond or a
triple bond. A double bond is a covalent bond that consists
of two pairs of shared electrons. Compounds that contain
two carbon atoms connected by a double bond are called
alkenes.
A triple bond is a covalent bond that consists of three
pairs of shared electrons. Hydrocarbons that contain two carbon atoms connected by a triple bond are called alkynes.
Hydrocarbons that contain double or triple bonds are
called unsaturated because the double or triple bond can be
broken to allow more atoms to be added to the molecule.
Examples of unsaturated hydrocarbons are shown in Figure 27.
H
H
H C C H
388
Chapter 15
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Aromatic Hydrocarbons Most
aromatic compounds are based on
benzene, the compound represented by the model in Figure 28.
Look for this structure to help
identify an aromatic hydrocarbon. As the name implies, aromatic hydrocarbons often have
strong odors and are therefore
used in such products as air fresheners and moth balls.
H
H
C
C
H
C
C
H
C
C
H
H
Figure 28 Benzene has a ring of six
carbons with alternating double and
single bonds. Benzene is the starting
material for manufacturing many
products, including medicines.
Other Organic Compounds
Many other types of organic compounds exist that have atoms
of halogens, oxygen, sulfur, and phosphorus in their molecules.
A few of these types of compounds and their uses are described
in the chart below.
Types and Uses of Organic Compounds
Type of compound
Uses
Examples
Alkyl halides
starting material for
Teflon
refrigerant (freon)
chloromethane (CH3Cl)
bromoethane (C2H5Br)
Alcohols
rubbing alcohol
gasoline additive
antifreeze
methanol (CH3OH)
ethanol (C2H5OH)
Organic acids
food preservatives
flavorings
ethanoic acid (CH3COOH)
propanoic acid (C2H5COOH)
Esters
flavorings
fragrances
clothing (polyester)
methyl ethanoate
(CH3COOCH3)
ethyl propanoate
(C2H5COOC2H5)
REVIEW
1. What is a hydrocarbon?
2. How many electrons are shared in a double bond? a triple
bond?
3. Comparing Concepts
rated hydrocarbons.
NSTA
TOPIC: Organic Compounds
GO TO: www.scilinks.org
sciLINKS NUMBER: HSTP375
Compare saturated and unsatu-
Chemical Compounds
Copyright © by Holt, Rinehart and Winston. All rights reserved.
389
Chapter Highlights
SECTION 1
Vocabulary
ionic compounds (p. 374)
covalent compounds (p. 375)
Section Notes
• Ionic compounds contain
ionic bonds and are composed of oppositely charged
ions arranged in a repeating
pattern called a crystal lattice.
• Ionic compounds tend to be
brittle, have high melting
points, and dissolve in water
to form solutions that conduct an electric current.
• Covalent compounds are
composed of elements that
are covalently bonded and
consist of independent
particles called molecules.
• Covalent compounds tend to
have low melting points. Most
do not dissolve well in water
and do not form solutions that
conduct an electric current.
SECTION 2
Vocabulary
• When dissolved in water,
acid (p. 377)
base (p. 379)
pH (p. 380)
salt (p. 382)
every molecule of a strong
acid or base breaks apart to
form ions. Few molecules of
weak acids and bases break
apart to form ions.
Section Notes
• When combined, an acid and
• An acid is a compound that
increases the number of
hydrogen ions in solution.
Acids taste sour, turn blue
litmus paper red, react with
metals to produce hydrogen
gas, and react with limestone
or baking soda to produce
carbon dioxide gas.
• A base is a compound that
increases the number of
hydroxide ions in solution.
Bases taste bitter, feel slippery, and turn red litmus
paper blue.
a base neutralize one another
to produce water and a salt.
• pH is a measure of hydronium ion concentration in a
solution. A pH of 7 indicates
a neutral substance. A pH of
less than 7 indicates an
acidic substance. A pH of
greater than 7 indicates a
basic substance.
• A salt is an ionic compound
formed from the positive ion
of a base and the negative
ion of an acid.
Labs
Cabbage Patch Indicators (p. 688)
Making Salt (p. 690)
Skills Check
Visual Understanding
LITMUS PAPER You can use the ability of acids
and bases to change the color of indicators to
identify a chemical as an acid or base. Litmus
is an indicator commonly used in schools.
Review Figures 8 and 10, which show how
the color of litmus paper is changed by an
acid and by a base.
390
pH SCALE Knowing whether
a substance is an acid or a
base can help explain
some of the properties of
the substance. The pH
scale shown in Figure
13 illustrates the pH
ranges for many
common substances.
Chapter 15
Copyright © by Holt, Rinehart and Winston. All rights reserved.
SECTION 3
Vocabulary
• Carbohydrates are
organic compounds (p. 383)
biochemicals (p. 384)
carbohydrates (p. 384)
lipids (p. 385)
proteins (p. 386)
nucleic acids (p. 387)
hydrocarbons (p. 388)
biochemicals that are
composed of one or
more simple sugars
bonded together; they are
used as a source of energy
and for energy storage.
• Lipids are biochemicals that
do not dissolve in water and
have many functions, including storing energy and making up cell membranes.
Section Notes
• Organic compounds are
covalent compounds composed of carbon-based
molecules.
• Proteins are biochemicals
that are composed of amino
acids and have many functions, including regulating
chemical activities, transporting and storing materials,
and providing structural
support.
• Each carbon atom forms four
bonds with other carbon
atoms or with atoms of other
elements to form straight
chains, branched chains,
or rings.
• Biochemicals are organic
• Nucleic acids are biochemi-
compounds made by living
things.
cals that store information
and help to build proteins
and other nucleic acids.
GO TO: go.hrw.com
Visit the HRW Web site for a variety of
learning tools related to this chapter.
Just type in the keyword:
KEYWORD: HSTCMP
• Hydrocarbons are organic
compounds composed of
only carbon and hydrogen.
• In a saturated hydrocarbon,
each carbon atom in the
molecule shares a single
bond with each of four
other atoms.
• In an unsaturated hydrocarbon, at least two carbon
atoms share a double bond
or a triple bond.
• Many aromatic hydrocarbons
are based on the six-carbon
ring of benzene.
• Other organic compounds,
including alkyl halides, alcohols, organic acids, and
esters, are formed by adding
atoms of other elements.
GO TO: www.scilinks.org
Visit the National Science Teachers Association on-line Web
site for Internet resources related to this chapter. Just type in
the sciLINKS number for more information about the topic:
TOPIC: Ionic Compounds
sciLINKS NUMBER: HSTP355
TOPIC: Covalent Compounds
sciLINKS NUMBER: HSTP360
TOPIC: Acids and Bases
sciLINKS NUMBER: HSTP365
TOPIC: Salts
sciLINKS NUMBER: HSTP370
TOPIC: Organic Compounds
sciLINKS NUMBER: HSTP375
Chemical Compounds
Copyright © by Holt, Rinehart and Winston. All rights reserved.
391
Chapter Review
USING VOCABULARY
To complete the following sentences, choose
the correct term from each pair of terms listed
below:
1. Compounds that have low melting points
and do not usually dissolve well in water
are ? . (ionic compounds or covalent
compounds)
2. A(n) ? turns red litmus paper blue.
(acid or base)
3.
? are composed of only carbon and
hydrogen. (Ionic compounds or
Hydrocarbons)
4. A biochemical composed of amino acids is
a ? . (lipid or protein)
5. A source of energy for living things can be
found in ? . (nucleic acids or
carbohydrates)
UNDERSTANDING CONCEPTS
Multiple Choice
6. Which of the following describes lipids?
a. used to store energy
b. do not dissolve in water
c. make up most of the cell membrane
d. all of the above
7. An acid reacts to produce carbon dioxide
when the acid is added to
a. water.
b. limestone.
c. salt.
d. sodium
hydroxide.
8. Which of the
following does NOT
describe ionic compounds?
a. high melting point
b. brittle
c. do not conduct electric currents in water
d. dissolve easily in water
9. An increase in the concentration of
hydronium ions in solution ? the pH.
a. raises
b. lowers
c. does not affect
d. doubles
10. Which of the following compounds makes
up the majority of cell membranes?
a. lipids
b. ionic compounds
c. acids
d. nucleic acids
11. The compounds that store information for
building proteins are
a. lipids.
b. hydrocarbons.
c. nucleic acids.
d. carbohydrates.
Short Answer
12. What type of compound would you use
to neutralize a solution of potassium
hydroxide?
13. Explain why the reaction of an acid with
a base is called neutralization.
14. What characteristic of carbon atoms helps
to explain the wide variety of organic
compounds?
15. Compare acids and bases based on the ion
produced when each compound is dissolved in water.
392
Chapter 15
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Concept Mapping
16. Use the following
terms to create a concept map: acid, base,
salt, neutral, pH.
CRITICAL THINKING AND
PROBLEM SOLVING
17. Fish give off the base ammonia, NH3, as
waste. How does the release of ammonia
affect the pH of the water in the aquarium? What can be done to correct the
problem?
INTERPRETING GRAPHICS
Study the structural formulas below, and then
answer the questions that follow.
H
H C H
H
C
H
C
C
a
H
C
C
H
C
c
b
H
H C
H C
H
H
H
H C H H
H C
C H
H C H H
H C H
H
H
H
C
C
H
C H
C H
H
H
d
H
H
H
C
H
C
H
H
C
C
H
H
H
22. A saturated hydrocarbon is represented by
which structural formula(s)?
23. An unsaturated hydrocarbon is represented by which structural formula(s)?
18. Many insects, such as fire ants, inject
formic acid, a weak acid, when they bite
or sting. Describe the type of compound
that should be used to treat the bite.
19. Organic compounds are also covalent
compounds. What properties would you
expect organic compounds to have as a
result?
20. Farmers often can taste their soil to determine whether the soil has the correct
acidity for their plants. How would taste
help the farmer determine the acidity of
the soil?
24. An aromatic hydrocarbon is represented
by which structural formula(s)?
Reading
Check-up
Take a minute to review
your answers to the
Pre-Reading Questions
found at the bottom
of page 372. Have your answers changed? If
necessary, revise your answers based on what
you have learned since you began this chapter.
21. A diet that includes a high level of lipids
is unhealthy. Why is a diet containing no
lipids also unhealthy?
Chemical Compounds
Copyright © by Holt, Rinehart and Winston. All rights reserved.
393
P
H
Y
S
I
C
A
L
S
C
I
E
N
C
E
•
L
I
F
E
S
C
I
E
N
C
E
Unique Compounds
What makes you unique? Would you believe it’s
a complex pattern of information found on the
deoxyribonucleic acid (DNA) in your cells? Well
it is! And by analyzing how this information is
arranged, scientists are finding clues about
human ancestry.
Mummy Knows Best
If you compare the DNA from an older species
and a more recent species, you can tell which
traits were passed on. To consider the question
of human evolution, scientists must use DNA
from older humans—like mummies. Molecular
archeologists study DNA from mummies in order
to understand human evolution at a molecular
level. Since well-preserved DNA fragments from
mummies are scarce, you might be wondering
why some ancient DNA fragments have been
preserved better than others.
Neutralizing Acids
The condition of preserved DNA fragments
depends on how the mummy was preserved. The
tannic acid—commonly found in peat bogs—that is
responsible for preserving mummies destroys
DNA. But if there are limestone rocks nearby, the
calcium carbonate from these rocks neutralizes
the tannic acid, thereby preserving the DNA.
Molecular Photocopying
When scientists find well-preserved DNA, they
make copies of it by using a technique called
polymerase chain reaction (PCR). PCR takes
advantage of polymerases to generate copies of
DNA fragments. Polymerases are found in all
living things, and their job is to make strands of
genetic material using existing strands as templates. That is why PCR is also called molecular
photocopying. But researchers who use this
technique risk contaminating the ancient DNA
with their own DNA. If even one skin cell falls
into the PCR mixture, the results are ruined.
Mysteries Solved?
PCR has been used to research ancient civilizations and peoples. For example, scientists found
an 8,000-year-old human brain in Florida. This
brain was preserved well enough for scientists to
analyze the DNA and to conclude that today’s
Native Americans are not direct descendants of
this group of people.
PCR has also been used to analyze the culture
of ancient peoples. When archeologists tested the
pigments used in 4,000-year-old paintings on
rocks along the Pecos River, in Texas, they found
DNA that was probably from bison. This was an
unexpected discovery because there were no
bison along the Pecos River when the paintings
were made. The archeologists have concluded,
therefore, that the artists must have tried very
hard to find this specific pigment for their paint.
This leads the archeologists to believe that the
paintings must have had some spiritual meaning.
On Your Own
394
DNA from mummies like this one provides
scientists with valuable information.
Research ways PCR is being used to detect
diseases and infections in humans and animals.
Copyright © by Holt, Rinehart and Winston. All rights reserved.
T H E S E C R ETS O F S P I D E R S I L K
What is as strong as steel, more elastic than a
rubber band, and able to stop a speeding bullet? Spider silk! Spiders make this silk to weave
their delicate but deadly webs.
this protein even closer, it looks like tangled
spaghetti. Scientists believe that this tangled
part makes the silk springy and a repeating
sequence of five amino acids makes the
protein stretchy.
Spinning Tails
Scientists think they have identified the piece
of DNA needed to make spider silk. Synthetic
silk can be made by copying a small part of this
DNA and inserting it into the bacterium
Escherichia coli. The bacteria read the gene and
make liquid silk protein. Biologists at the
University of Wyoming, in Laramie, have come
up with a way to spin spider silk into threads
by pushing the liquid protein through fine tubes.
What Do You Think?
A golden orb-weaving spider on its web
The Tangled Web We Weave
If you’ve seen a spider web, you’ve probably
noticed that it resembles a bicycle wheel. The
“spokes” of the web are made of a silk thread
called dragline silk. The sticky, stretchy part of
the web is called capture silk because that’s
what spiders use to capture their prey. Spider
silk is made of proteins, and these proteins are
made of blocks of amino acids.
There are 20 naturally occurring amino
acids, but spider silk has only seven of them.
Until recently, scientists knew what the silk is
made of, but they didn’t know how these
amino acids were distributed throughout the
protein chains.
Scientists used a technique called nuclear
magnetic resonance (NMR) to see the structure
of dragline silk. The silk fiber is made of two
tough strands of alanine–rich protein embedded in a glycine–rich substance. If you look at
Scientists seem to think that there are many
uses for synthetic spider silk. Make a list in your
ScienceLog of as many things as you can think
of that this material would be good for.
Spiders use organs called spinnerets to
spin their webs. This image of spinnerets
was taken with a scanning electron
microscope.
395
Copyright © by Holt, Rinehart and Winston. All rights reserved.